For efficient signal transmission in an optical system, components, such as optical fibers, lasers, mirrors, lenses, microelectromechanical (MEMS) devices, isolators, modulators, and detectors, must be positioned accurately and reliably. For example, in a fiber-coupled laser module, a laser and an optical fiber must be positioned in mutual alignment to obtain a high coupling efficiency. However, accurate positioning of such components is difficult to achieve and maintain.
To facilitate their positioning, such components are often attached to a substrate through a mount. The mount is attached to the substrate, and the component is attached to the mount, forming a component assembly. In the fabrication of a such a component assembly, the component is, typically, soldered to the mount by using a heating means to melt a solder.
The mount may be fabricated from a variety of materials, but ceramic materials are particularly suitable, owing to their advantageous thermal and mechanical characteristics. For example, a mount composed of silica (SiO2), as disclosed in U.S. Pat. No. 4,523,802 to Sakaguchi, et al., alumina (Al2O3), as disclosed in U.S. Pat. No. 6,679,636 to Gilman, et al., or silicon carbide (SiC), as disclosed in U.S. Pat. Nos. 6,883,978 and 7,284,913 to Powers, may be used to attach an optical fiber to a substrate by soldering. In addition, the use of a mount composed of silica, zirconia (ZrO2), macor, or M120 to attach an optical fiber to a substrate by soldering is disclosed in U.S. Pat. No. 6,758,610 to Ziari et al., which is owned by the assignee of the present invention and is incorporated herein by reference.
For another example, a mount composed of beryllia (BeO), boron nitride (BN), aluminum nitride (AlN), or silicon carbide may be used to attach a laser to a substrate, as disclosed in U.S. Pat. No. 6,758,610 to Ziari et al. The use of a mount composed of aluminum nitride to attach a laser to a substrate by soldering is also disclosed in U.S. Pat. No. 6,720,582 to Miyokawa, et al. and U.S. Pat. No. 6,961,357 to Moriya, et al.
Furthermore, a surface of the mount may be metallized for various functions. For example, to promote adhesion of the solder to the mount, the mount may be coated with a layer or a pattern of a metal wettable by the solder, such as gold, as disclosed in U.S. Pat. No. 6,292,499 to Pearson, et al., U.S. Pat. No. 6,720,582 to Miyokawa, et al., and U.S. Pat. No. 6,758,610 to Ziari et al. To provide a barrier to the solder, the mount may be further coated with a layer of a metal non-wettable by the solder, such as titanium, as disclosed in U.S. Pat. No. 6,758,610 to Ziari et al. When a light source, such as a laser, is used as the heating means to melt the solder, a mount composed of an optically non-absorptive ceramic material may be coated with layer of an optically absorptive metal, such as titanium, to enable the mount to be heated by light from the light source, as disclosed in U.S. Pat. No. 6,758,610 to Ziari et al. Disadvantageously, such layers of an optically absorptive metal are easily burned when heated by light from a laser, which limits their applicability to mounts composed of materials having very low thermal conductivities.
An object of the present invention is to overcome the shortcomings of the prior art by providing a component assembly including a mount optimized for soldering using a light source, as well as a method for fabricating such a component assembly. Most importantly, the mount is composed of a ceramic material having properties advantageous for soldering using a light source. The ceramic material is optically absorptive to enable the mount to be heated by light from the light source during soldering, aiding to melt the solder used to attach the component to the mount. Optical absorption by the ceramic material also prevents burning by the light source, allowing ceramic materials having a wide range of thermal conductivities to be used for the mount. Furthermore, the thermal conductivity of the ceramic material is significantly lower at the melting point of the solder than at the operating temperature of the component. Accordingly, the mount retains heat during soldering, facilitating melting of the solder to create the attachment, but dissipates heat during operation, hindering undesired softening of the solder and, thus, improving the reliability of the attachment.